Seagrass is the common term for a broad class of underwater plants that grow in coastal zones. Seagrasses are generally tall and green, and grow across large underwater areas. These underwater areas resemble meadows—thus the term seagrass.
Seagrasses create energy using photosynthesis, and thus need sun. As a result seagrass does best in shallow water.
The importance of seagrass to the aquatic ecosystem is difficult to overstate. Seagrass provides food for marine life, a nursery for both adult and juvenile invertebrates and vertebrates, a natural wavebreak by absorbing the energy of incoming water, a stabilizing layer for the sand and soil, and after death the decomposition supports yet more forms of aquatic life. Seagrass also sequesters carbon and captures nutrients from the surrounding aquatic environment.
Seagrass is sometimes likened to the aquatic equivalent of the terrestrial rainforests. As with rainforests, preservation is critical.
In the U.S., seagrass is concentrated in the Gulf of Mexico, coasts of Florida, and south along Central America to Columbia and Venezuela in South America.
Restoration work in the U.S. is concentrated around Florida because of Florida's large number of boaters, and the damage that results from negligent boating.
Florida species of seagrass include:
Scientific nameCommon nameThalassia testudinumTurtle grassHalophila engelmanniiStar grassHalophila decipiensPaddle grassHalodule beaudetteiShoal grassHalophila johnsoniiJohnson's seagrassSyringodium filiformeManatee grassRuppia maritimaWidgeon grass
Different species of seagrass are native to different areas of the world.
The survival of seagrass is under constant threat. Harm to seagrass comes in the form of environmental damage as a result of overdevelopment, and physical damages from boaters.
Boaters are a great hazard to seagrass due to its preference for shallow water. Additionally, boaters often have trouble determining whether a given stretch of water is deep enough because depth varies due to tide and currents. Damage to seagrass by boating results in prop scars and blowholes.
Prop scars are caused by contact between the propeller/rudder/outdrive of a boat and the seagrass/sand. When viewed from overhead, prop scarring appears as long lines of sand amidst areas of green seagrass, drawing the analogy to a scar.
The result of the damage is a depression in the sand that creates a trench, destroys the seagrass, and displaces the sand.
Boat damage may also create blow holes. A blow hole is caused when a boat has become stuck and the operator attempts to free the boat by running the boat at high throttle. The resulting prop wash from the propeller pushes the sand away from the area behind the propeller, creating a hole.
As compared to prop scars, blow holes are round and deep, rather than long and shallow.
For both prop scars and blowholes the sand and vegetation displaced during formation may create a berm, or elevated perimeter, around the damage. This displaced sand may bury nearby seagrass, causing further damage.
When viewed from above the damage caused by a prop scar or blowhole can be seen as current carries away the now-exposed sand. The loose sand blows across the field of seagrass, much like smoke from a fireline.
Any damage to seagrass reduces its ability to sustain its local environment, depressing fish stocks and stressing the ecosystem. Thus, recovery as quickly as possible is key to limiting damage.
Without intervention, prop scars recover in one year, if minor, or as long as sixty years for severely damaged areas. Deep scars require particularly long periods of time for recovery because the newly-exposed sediment does not readily support the growth of seagrass, and without seagrass roots to stabilize the soil it is prone to washing away.
Given this difficult environment, what is needed is a process and apparatus for the restoration of damaged seagrass.